Rocks recently uncovered from beneath prehistoric ice have exposed a concerning reality: tropical glaciers have shrunk to their smallest size in over 11,700 years. This discovery, published in the journal Science by researchers from Boston College, signals that the tropical regions have warmed beyond limits last seen during the early Holocene epoch.
RAPID GLACIAL RETREAT SURPASSES PREDICTIONS
Scientists have long predicted that glaciers would retreat as global temperatures rise, particularly in tropical regions near the equator. However, new evidence from the Andes Mountains indicates that this glacial retreat has occurred much faster than anticipated. Boston College Associate Professor Jeremy Shakun, a paleoclimatologist and co-author of the study, explained that the retreat has already surpassed a critical benchmark across epochs.
“We have strong evidence that these glaciers are smaller now than they have been at any time in the past 11,000 years,” said Shakun. This rapid reduction is primarily due to rising temperatures, rather than other factors like reduced snowfall or changes in cloud cover. The findings suggest the tropics have warmed beyond their historical Holocene range, marking a significant transition into the Anthropocene.
TRANSITION FROM HOLOCENE TO ANTHROPOCENE
The Holocene epoch, beginning around 11,700 years ago, was a period of relative climate stability that saw the rise of human civilization. Glaciers during this time played a crucial role in shaping the Earth’s landscape and influencing water flow and sea levels. However, the current state of these glaciers suggests they may now belong to the Anthropocene—an epoch characterized by significant human impact on the Earth’s geology and ecosystems.
This shift not only reclassifies the glaciers but also indicates a broader, more alarming trend of accelerated glacial retreat. The findings suggest that other glaciers worldwide may also be retreating faster than predicted, potentially leading to devastating environmental and societal impacts much sooner than expected.
THE “CANARY IN THE COAL MINE”
Shakun referred to this development as a “canary in the coal mine” for glaciers worldwide. While glaciers have been retreating globally over the past century, the magnitude and speed of this retreat, compared to natural fluctuations over millennia, have remained unclear. The study aimed to determine how small tropical glaciers are today compared to their size over the last 11,000 years.
METHODOLOGY: MEASURING THE UNCOVERED BEDROCK
The research team, comprising scientists from Boston College and several international institutions, conducted field studies in Colombia, Peru, and Bolivia. They analyzed bedrock recently exposed by the retreating glaciers in the tropical Andes. By measuring the presence of rare isotopes—beryllium-10 and carbon-14—in these rocks, the researchers could determine how long the bedrock had been exposed to cosmic radiation, which helped them infer the historical size of the glaciers.
“By measuring the concentrations of these isotopes in the recently exposed bedrock, we can determine how much time in the past the bedrock was exposed, which tells us how often the glaciers were smaller than today,” explained Shakun. The absence of significant amounts of these isotopes in the 18 bedrock samples studied indicated that these glaciers have not been this small since the last ice age.
HISTORICAL CONTEXT: COMPARING PAST AND PRESENT RETREATS
Twenty years ago, research at the Quelccaya Ice Cap in Peru— the world’s largest tropical ice mass—revealed plant remains dating back 5,000 years, uncovered as the glacier retreated. This suggested that Quelccaya had remained larger than its current size throughout that period. These earlier findings indicated that modern ice retreat was unusually significant, though not yet at a critical level compared to the entire Holocene period.
However, Shakun’s recent study applied a more comprehensive approach, examining multiple glaciers and utilizing techniques that provided unambiguous evidence of past glacial sizes. This method offers a clearer understanding of how unprecedented the current retreat is.
IMPLICATIONS FOR THE FUTURE OF GLACIERS
The research team’s work extends beyond the tropics. They have applied similar techniques to glaciers across the entire American Cordillera, a mountain range stretching from Alaska to Tierra del Fuego. The team’s findings from North America were published last year, and they plan to release results from southern South America soon.
“Once we do that, these studies can all be put together into a global perspective on the current state of glacier retreat,” said Shakun. This global perspective is crucial for understanding the broader implications of glacial retreat and its impact on sea levels, freshwater resources, and ecosystems.
AN URGENT CALL TO ACTION
The findings from the Andes are a stark reminder of the accelerating pace of climate change and its far-reaching effects. The shrinking of tropical glaciers to sizes not seen in over 11,700 years highlights the urgency of addressing global warming. As the world moves further into the Anthropocene, the need for comprehensive climate action becomes increasingly critical to mitigate the impact on glaciers and the broader environment.
Understanding the full extent of glacial retreat requires continued research and collaboration across disciplines and regions. The work of Shakun and his colleagues represents a significant step towards this understanding, offering vital insights into the current state of the Earth’s climate and the challenges that lie ahead.
As we continue to witness the effects of climate change on our planet, the shrinking tropical glaciers serve as a powerful symbol of the urgent need to address this global crisis. Only through concerted efforts can we hope to slow down or reverse the damage and protect the natural world for future generations.